Radio telephone and telegraph system



Feb. 2, 1932. A. BAILEY RADIO TELEPHONE AND TELEGRAPH SYSTEM Filed Dec. 13, 1928 INVENTOR azlgy BY ATTORNEY Patented Feb. 2, i932 AUSTN BAILEY, 0F hAPLEWOOD, NEW JERSEY, ASSGNOR TO AMERICAN TELEPENE f AND TELEGRAPH COIVLPANY, A CQR-PQRATZON 0F NEW YORK Unirse sra'res rarer www..

RADIO TELEPHONE .AND TELEGEAPI-I SYSTEM Application led December 13, 1923. Serial No.'325,82'?.

This invention relates to the transmission der to receive telegraph messages the teleof signals, and more particularly to arrangegraph receiver was associated with the one-v meuts for utilizing the radio apparatusof a ivay line leading from the radio receiver at radio telephone system for the transmission a point between the radio receiver and the 5 ot telegraph signals. point at which the disabling means was ap- Vfhere a radio link is used for establishing plied to the one-Way line, so that the fact telephone connections between two distant that the line as a Whole Was disabled, so far points such as, for example, New York and as transmission from the radio receiver to the London, it is desirable to utilize the radio ap telephone switching point was Concerned, did

:u paratus, which is normally employed forteienot prevent reception of telegraph messages se phone transmission, for the transmission oi over the non-disabled portion ot the one-Way telegraph messages when the apparatus is not lille'. An audible tone 0f a different fre- Qmployed for telephone purposes. It is parquency was used to modulate the carrier and ticularly desirable to use the radio telephone was then transmitted from the distant termik 5 apparatus for the transmission of telegraphic Dal 0f the ril CliO link. This t0n@ Was then demessages between operators in connection tectcd and reproduced by the radio receiver with the establishment 0f telephone conin a manner similar to the reproduction of ne'ctions. ordinary telephone currents, and upon being Heretotore such telegraph operation has selectively transmitted from the one-Way rc- -'i been carried out upon a halt-duplex basis; @Giving line t0 the telegraph T'CeVel WS 'ZG that is, While messages could be' transmit- ClUSGd t0 Operate the telegraph receiver in a ted over the radio links in either direction, WGH-known Ina-111161'.

they'were actually transmitted in only one VVhl@ the f0leg0ng Mllgmnt PCT- direction at a time. This Was accomplished Hl'ltd the U'HSmSSOU 0f telegraph m95 as fllowg; The radio transmit/Cei; and radio sages one Way at a time, it is highly desirable 75 receiver at one end of the radio link were to be able to transmit the telegraph messages located some distance apart and connected by GH a full-duplex basis so that telegraph transseparate one-way lines t0 a. common sivitchmission may take place in both directions siingpoint at which connections could be csmultaneously. It might be supposed that .o tablished to any desired telephone line. this Would be'cnt-irely possible Where audible an Eachone-Way line Was provided with voicetones of different frequencies are employed controlled apparatus whereby when rtelefor ltransmiting the telegraph messages to the phonev currents' were transmitted over the radio transmitter and for receiving the teleline leading tothe radio transmitter, the onegraph messages from the radio receiver, but 37 wayline leading from the radio receiver'vvas experience show s that such is not the case. 8:/ disabled, and vice versa. This was neces- Due to the fact that the radio receiver is Vsary in order to obtain propertclephone opnearer to the local radio transmitter than it eration. lclegraph messages were transis to the distant radio transmitter, it tremitted by impressing an audible tone, interw quently receives more energy from the local rupted in accordance with the message, upon transmitter than from the distant transmitter, 9F the telephone terminal at the telephone even When slightly different radio Wave switching point. The connection et the telelengths are employed for transmission in the graph transmitter at this point automatically tivo directions and the receiving system is operated'the voice-controlled devices to renmade highly selective to the Wave length cnif 45 der the one-Way line connected to the radio ployed by the distant transmitter by employ- 9L transmitter operative and to disable the line ing directional antenna systems. Under leading` from the radio receiver. The ardig these conditions the telegraph message being ble tone Was then modulated upon thecarsent over the one-Way line leading to the rarier Wave of the radio transmitter in the dio transmitter received on the one-Way 50 same manneras telephone currents. In orline leading from the radio receiver simulta- 100 neously with the telegraph message trom the distant station. lhile the telegraph receiving apparatus associated with the receiving line is able to discriminate by 'frequency seleetion between the two tones corresponding to the sending and received telegraph signals, it has been found that when the energy of the undesired signal exceeds certain limits the one-way amplifiers included inthe oneY way receiving' line between the radio receiver and the telegraph receiver are overloaded, thereby causingdistortion of the desired signals. This distortion is so great aste cause false signals, particularly when printing telegi'aphmessages are transmitted.

.In order to overcome this diiiculty itis proposed, in accordance withtlie present in'- telegraph signals are being' received from the'v local transmitter and to again cut the suppression ,device out when such telegraph sig- `nals ceaseY or fall below a harmtul'value.

vtha .durin's whicna.

This is accomplished by selecting from the radio receiver some ot the energy of the tone corresponding to the signalsfrom lthe local transmitter, 'rectifying the energy and causing it to operate a relay arrangement for cutting the filter in and out. As this arrange-Y ment should not be'responsive to telephone currents or static signals or the same frequencies as the tone employed for telegraph transmission, the relay arrangement Vlor switching` the filter inandout is designed tov yoperate only when thetone tretpiency received over an interval of time longer than l Avtelephone sie' alor a 'ranges'tatic signal would persist, andthe a ment has a sutlicient hang-overse lwhen it isl once loperated to .cut in the filter, it will be maintained operated duringY interruptions ofthe tone such aswould occur in connection with the transmission of theV signals of a telegraph message.

New in any telegraph system employing two currents differing' in frequency oi' intensity, for transmission, the code may be con- YsideredV as beingl made up oil marks and spaces. In 4ordinary land Vwire Morse or printer operatiomthe circuit in its idle condition transmits a continuous marking signal. ln radio telegraphy, the circuit when in the idle condition customarily transmits a spacing signal. lf any ordinary Morse oi' printer transmitter is usedvin connection with he arraiifjrenient'aboveV described so that no tone is transmitted during` its marking interval,

' the idle periods will nevertheless be considrangement embodying'the principles of the ln the drawing', the circuit Vai'-V invention. rangement and apparatus 'at one terminal only of theradio link is shown, it being; undei'stood'that the'apparatus at theother terminal will be similar to that illustrated."

Referring to the drawing, a radio trans mitter is conventionally indicated at T, and similarly a radio" receiver is conventionally indicated at R. The receiver and transi'nitter are located some distance apart in yorder to reduce interference in the receiver from the local transmitter; The radio receiver yand radio transmitter are connected by means of a `four-wirev circuit to a telephone office at which switching connections are established to any desired telephone circuit by means of a cord C, which may connect the terminal jack .l of the four-wire circuit with a liack J of a desired telephone line by means of the plugs P and P. The four-wire circuit comprises one-way lines TL and RL connected together at the telephone yoffice through a hybrid coil 10 and balancing network N, ina well-known manner. The linesv TL and RL are one-way lines, the line TL being arranged to transmit from the terminal Vjack J to the radio transmitter T andthe line RL being arranged to transmit from the radio' receiver'lt to the jack J; Either oi' both of these lines may include a'number of repeatersV (not shown) for amplifying the telephone currents transmitted thereover. In orderfto prevent singing over the overall our-wire circuit including the radio paths tothe distant terminal, and also to prevent singing over the local circuit fromthe transmitter Tf to the receiver R,"over theline RL, through the hybrid'c'oil 10,'and over the line TL to, theradio transmit*er,'the line TL is normally disabled. Voice-operated devices are provided whereby whentransmission takes place from the jack J over tlieline TL tothe transmitter T, the line TL is put in operative condition and the Vline RL is disabled. When, however, transmission takes place from the receiver VIt over the line RL, to the jack J, the line TL is maintained disabled. vThis is accomplished by associating with each one-way line a voice-operated device for controlling a short-circuit across the other line. ln the case of the line TL this apparatus comprises an xamplifier-'detector unit` of Welt-known type Yio TV 'assoeiatediwitfh the line TIL, said'unit con-- trolling relays TVR- and TVR.. When voice currents enter" the amplifier-detector TVT, the relays TVRand'llVR are energized, the latter opening-the normali short-circuit aeross-tlieline andper-mitting transmissien JCo-tale place froml jfacli@ J tothe-transmitter T, and the former closing a` shortcircuit acrossl thelinet and the input terminalsl ofiA an amplifier-detector unit RV associated with tlie lineRL.v K

l'llhe'ainpliier-detector: unit RV is associatedwith the line RE-andrespond's to voice' currents receivedIk from the radio receiver R' andl Jtransmitted overjthe" line RL to energize-a relay RVRin' af Well-known manner, so that th-e latter short-circuits the line TL ind-.ependentl'y et" the normal. short-circuit' controlled byl theI relay TVR. The shortcircuittlius appliedtethelin'e TL also serves to short-circuit theamplifiertdetector TV te prevent false' operation. Eelay net-Works TllifandlR-DN are asseciatediwithi the lines- 'llli and-RL, respectively, to-enable the voicecont lied? switching" devices to perform their ciiiccs before the Vvoi'eecur-rents arrive at the peints in the circuits which are affected by the switching'operatiensg For example, when voice v currents are transmittedz from the jack J 'overthe lineT-L, thevei'ce currents aresutciently. delayed inV passing' througlithe netwerk TEN to enable the amplifier-detector unit T to remove the short-circuit from theY line TL before. the voicecurrents arrive at' the p oint at which-it isapplied. Similarly, when voice currents are transmitted from the receiver R over the line RL, theV voice cur-A rents are suiiiciently delayed by the network rl to enable-the amplifier-detector RV to sli rt-circuit the lineTL betere the voice curre shave an opportunity to pass through thev hyarid ceil l0v (due to unha/lance)y and enter the line TL. ,Y

During periods when the-circuit above dcscribed is not being usecl for telephone operationit' is desirable to use the radio facilities for the transmission of telegraph messages, and more particularly it is desirable to trans- 'mit printer messages between operators to give directions necessary to the establishment ot telephoneconnections over the radio linlr. ln order't'otransmit such telegraph messages from the telephone oiice shown, to a distant telephone office associated with the distant terminal et the radio link, the cerd'C.y which is usedA for settingv up telephone connectiens,may have its plug l?" inserte( in a jackV JQ which is connected to a telegraph transmitter. This transmitter may comprise a'transmittingprinter unit conventionally inf dicated at T which, by means of marking andspacing'signals, controls'a relay TR. The

contact otthis relay is arranged to-open and close a= short-circuit across theterminals of a" tonesource Gconnectedito the tip andring conductoroi the j ack J The relay TR has its contact' se arranged as-to closethe-shortcircuit across the tone source G during-marking'impulses, and to open the short-circuit during spacing' impulses. Consequently, an audible tone vwill be appliedito the terminals` of? the jack Jf and transmitted over-the line TL to the radio transmitter during the spacingintervals,.while marking signals will be represented by a 11o-tene condition ot the circuit.. The tone employed is preferably an audio frequency so that it may lie-transmitted over the circuit. TL in the same manner as veice=currents are transmitted.

Since,` as has already been described, the line TL. isA normally disabled by means of. the short-circuit applied by the relay TVR', itis necessary tor render the connection over the line TL operative in order that the printer signals may be transmitted rlhis result is accomplished by' a ground connection established over the sleeve conductor or. the j ack J, plug'l?, sleeveconductor of the core'C, sleeve conductors ot the plug P', andthe telegraph jack: J", and' thence over a. conductor 20` through the windings ofthe relays TVR and TVR" to the plate battery. This causes the energization' etl relays TVR and TVR independently ot.' the plate circuitk of theV amplifier-detector unit TV and maintainsthese relays-operated aslong as the telegraph connection is established.' The short-circuit is, therefore, removed from the'line TL so that the tone corresponding-to the spacing. signals may betnansmitted over the line TL to the radio-transmitter T, where it is modulated upon. the radio carrier in the same way as ordinary telephone currents, and transmitted to the radio receiver at the distant ra dio-y terminal;` The energization ot the relay TVR, however, short-circuits the line RL between thel ampliiier RA andthe delay network. RDN so that transmission cannot take place freni the' radio receiver R over the line RL to the jack J It is, therefore,.neces sary tliatthe telegraph receivingapparatus be associated'with the line RL for reception of telegraph signals from the distantv station in suchl manner as'not to be affected by the short-circuit controlled` by the relay TVR. Accordingly, such al telegraph receiving apparatus is bridged acrossl the line RL at m-ylbetwcen the point at which the short circuit is applied and the receiver R. The one-Way.A amplifier RA is then connected between the terminals m-v-y of the telegraph receiving apparatus and the point at which the short-circuit is applied by the relay TVR', So-that the short-circuit docs notr have Accordingly, such a telegraph receiving apparatus and transmission may take place Jfrom the radio receiver R over the line RL. toit-he termials :z2-y and thence into the telegraphv receiving apparatus..

The telegraph signals received from the distant radio transmitter are applied to such radio transmitter as an interrupted tone'in a manner similarv to that already ldescribed with respect to the station shown, but in this instance the Vtone will have a' diierent frequency from that generated by the tone source G. The tone employed at the distant station is modulated upon the carrier. and transmitted tothe receiver R where it is demodulated and transmitted over the line RL.

to the telegraph receiving apparatus connected at .0c-y., In order that the telegraph receivingapparatus may distinguish between this tone and the tone correspondinglto` the source G, which may 'appear in the output circuit of the radio receiverR dueto interference from the local transmitter T, such telegraphreceiving apparatus includes a lilter RF for selecting the desired tone. An ampliiier RA may also be provided for amplifying the received current, and a detector RD ot well-known type is provided for Y rectifying the tone to produce direct current signals corresponding to the telegraph impulses.Y The direct current impulses `actuat/e the receiving relay RRl, as will bel described in more detail later, and by vmeans of this relay are transmitted to the receivingprinter conventionally indicated at'RP, as will also be made clear later. i

The arrangementso fary described will opi erate satisfactorily tor half-duplexV operation where' the circuit is only used for the transmission of telegraph messages in one direction at any one time. In attempting to operate the circuit on a full-duplex basis so Y that transmission of telegraph messages takes place in both directionsat .the same time,

however, dithculty may be encountered wherel interference trom the local transmitter T is very heavy, due to the tact that the signals from' the local transmitter T, when transmitted over the line RL at the same time as the desired signalsfrom the distant transmitting station,will tend to overload the repeaters (not shown) in the line RL, and thereby z cause-'distortion 'ot the desired signals actuallyreceived by thel telegraph receiving apparatus. lt therefore becomes necessary' to suppress from the line RL theV tone frequency corresponding to thetone source ,GL This is Vaccomplished byj switching intolthe line Y Y would occur during the transmission of telef RL on the output vside ofthe -radioreceiver R a: suppression lilter RSF` ot any Vwell- .lrnown type, so designed as to suppress trom n thelineRL the tone frequency corresponding to the-sourceG, while freely passing other cuit during telephone transmission would tend to suppress from the telephone band frequencies in the neighborhood of the tone from the source G, thereby causing telephonie distorti on, the arrangement should be such that.

byselecting some otjthe'energy of the undesired tone from-the local-transmitter T on the output side'oifthe radio receiver R and applying the selected energy `to a detector which operates switching relays, to switch the filter in and -out o t the circuit. Accordingly, a circuit is bridged across the terminals -y, which comprises an amplifier RA for amplifying the unwanted tone trequency, a selecting iilter RF fory selecting such unwanted tone frequency anda vacuum tube-detector RD in whose plate circuit are connectedv relays RRl, RRZv and RRQ. These inlays are normally energized by the' plate current flowing through thetube RD, and the relays RRl. and RR2 Vnormally connect the receiver R through tothe line RL independently- O the Asuppression `filter RSF. l/Vhen the selected tone is applied to the grid ot the tube RD, however, the plate current is reduced so that the relays are ole-energized, relays RR1 and RRZ interpolating the suppression lilter VRSF between the receiver R andthe line RL, while the relay RR3 closes the circuit ota signal lamp 30, which indicates that the suppression filter is in circuit.

The relay arrangement above described should be so designed as to prevent false operation due to relatively short telephone andstatic signals involving frequencies cor- Y responding to the tone frequency selected by the filter RSF. ln order to accomplish this result, the condenser l() and grid leak resistance 50, which are connected to the grid circuit ot the tube RD, are so proportioned that the negative potential built up on the grid in response, to the alternating current tone frequency is `built upso gradually that the relays, such as RR1 and RR2, do not release to cut in the filter RSF until a period has elapsed longer than an ordinary telephone or staticsignal would persist. The elements 40 and 50 also serve to prevent the rnegative charge built up on the gridV from leaking oli' and thereby increasing the plate current suiii- Aciently to again energize the relays RR1, RRZ

and RR3 until a time has elapsed att-er the cessation of the tone whichis slightly greater than the longest tone ,interruption which erated to switch in the'suppressien filter in response to theirst spacing signal transmitted after the Vin irinting telegraph transmitter is applied at the Jack J. Also, when CII 4Q- transmission of messages will be preceded by the transmitter isapplied to the jack J without sending any signals, no tonevwill be'applied since the marking condition is a notone condition. Accordingly, some provision must be made for applying a tone to the circuit after the telegraph transmitter has been connected and just before the transmission of telegraph signals begins, t iis tone being sustained long enough to build up a negative potential on the grid of the detector tube RD to release the relays BB1 andltl2 and connect the filter RSF in circuit. For this purposea switch maybe provided for connecting the, transmitting printerrTP to the transmitting -relay Tilt. l switch 60 to its dotted line position after the teleg 'aphtransmitter has been plugged upto the jack J and just before the transmitter starts to send signals, a spacing current will be applied to the transmitting relay TR, thereby removing the short-circuit ,from the tone Vsource G long enough to transmit the tone frequency to cut inthe suppression lter RSF, is soon as the transmitting 'printer is ready to transmit signals, the switch 60 is thrown to itslower position, and the ensuing transmission of interrupted spacing signais serves to maintain the suppression filter in circuit. VJ hen the transmitting printer TPy is not operated for an appreciable length of time or when it is disconnected by withdrawing the plug P from the jack J, the transmission of the tone frequency ceases, and.`

after the hang-over period has elapsed, the

j relays BB1, RR2 and BB3 areagain energized and the suppression filter is cut out of cir-cuit.v

Whenever the telegraph transmitter at they distant station is applied to the circuit, the

the transmission of a sustained tone to operate the local arrangement at the distant receiving station fork cutting in the suppression filter. This tone will then be followed by an interrupted tone corresponding to themessage. The tone frequency employed at the `distant station will be different from that generated by the source G and will be applied to the distant radio transmitter to modulate 5G the carrier in the same manner as a telephone signal. The carrier isreceived by the radio receiver R, which detects therefrom the tone frequency and transmits it over the line RL to vthe y telegraphv receiving apparatus con- '.55 nected at the point -y. This receiving apparatus comprises .an amplifier RA for amplifying the desired tone, a filter' RF for selecting the tone corresponding to the distant transmitter and a detector RD for rectifyingthe ktone to operate the receivingl relay RRQ. The initial sustained tone for operating the lsuppression filter causes the relay RRQ to transmit to the receiving printer RP a spacing signal,.which may cause one or By throwing the;

l. In a radio signaling system including a radio :transmission link, a radio transmitter and a radio receiver at one terminal of said radio link, a four-wire junction, a normally disabled one-.way transmitting line extending from said four-wire junction to said radio transmitter, a one-way receiving line extending from said radio receiver to said junction,

means associated with each of said lines and p responsive to telephone signals transmitted thereover to disable the other line, telegraph transmitting apparatus and telegraph receiving' apparatus, means responsive to the application of telegraph signals from said telegraph transmitting apparatus to said fourwire junction to render said transmitting line operative and to disable said receiving line, means connecting said telegraph receiving apparatus with said receiving line between the point at which it is disabled and said radio receiver, a suppression device associated with said radio receiver for suppressing telegraph signals received from the local radio transmitter while passing telegraph signals received from the radio transmitter at the distant end of the radio link, and means responsive to telegraph signals received by said radio receiver from the local radio transmitter to connect said suppression device in said receiving line.

2. ln a radio signaling system including a radio transmission link, a radio transmitter and a radioreceiver at one terminal of said radio link, a four-wire junction, a normally disabled one-way transmitting line extending from said four-wire junction to said radio transmitter, a one-way receiving line extending from said radio receiver to said junction, means associated with each of said lines and responsive to telephone signals transmitted thereover to disable the other line, telegraph transmitting apparatus and telegraph receiving apparatus, means responsive to the ap- I plication of telegraph signals from said telemitter VWhile passing telegra-pli signals received trointlie radio transmitter at the distant end ci' the radio linkand means to coniiect said suppression device in said receiving li e, said means operating in response to a sustained signal of predetermined transmitter, alone-Way receiving line extend. ing froml said radio receiver to saidjunction,

means associated with each of said lines and responsive to telephone signals transmitted thereover toA disablethe other line, telegraph .transmitting-apparatus and telegraph receiving apparatus,means responsive to the application of telegraph signals from said telegraph transmittingapparatus to said four-f Wire junction tti-render said transmitting line operative'and/to disable said receiving line,

means connecting said telegraph receiving apparatus with said receiving line between the point at which it is- ,disabledV and said radio receiver, a suppression device associated vvvith said radio receiver for suppressing telegraph signals received Vfrom the local radio transmitter While passing telegraph signals received from the radio transmitter at the distant end of the radio link, and means to-conneet said suppression `device in said receiving line, said means operating in' responseA to a sustained signal of predetermined length received bythe local radio receiver from the local radio transmitter, saidmeans operating to maintain said suppression device connect-` ed during code interruptions. f Y

4:. In a radio signaling system including a radio transmission'link, a radio transmitter and a radio receiverat one terminal` of 'said radioY link, a four-Wire junction, va normally disabled vone-Way transmitting line extending from said four-Wire junction to said dradio transmitter, a one-Way receiving-line extending from said'radio receiver to said junction, means associated with each ot saidV lines and responsive to telephone signals transmitted thereover to disable the other yline,':telegraph transmitting apparatus andv telegraph receiving apparatus, said tele-1v graphl transmitting apparatus producing a.

toneinterrupted. in accordancevvith a code, yand said telegraph receivingl apparatus including means to translate an interrupted tone oit'ditferent frequency received from the distant terminal into telegraph signals,

means operating when the telegraph transmitting apparatus is associated With said four-Wire junction to renderfsfaidv transmitting line operative and to disable said receiving line, means-'connecting said telegraph receiving lapparatus--Witli'i` said receiving line betvveen the point'at'vvh-ich it is disabled and said'radio receiver, a suppression device for suppressing the tone `irequr'ency supplied byA said telegraph transmitting apparatus While lpassing the tone frequency 'used for tele-- gra-ph'transmission from the distant terminal, and means responsive to the tone transmitted by radio from the 'local-radio' transmitter to the local radio receiver to connect said suppression device in said receivingvlinej -5. Ina radio signaling'system including aV radio transmission link, va radio transmitter and a radio receiver at one terminal of said radio link, a four-Wire junction, afnorinally disabled one-Way transmitting lineextending from said four-Wire vjunction to said radiotransinitter, a one-Way receiving line eX- tendingfrom said radio receiver to said junction, means associated With each of'y said lines ,and V responsive to telephone signals transmitted 'thereover toA disable t'lieother line, telegraph transmitting Vapp aratusand telegraph receivinfra aratus said tele ra h'transmitvting apparatus producing a tone interrupted in accordance With a code, and said telegraph receiving,v apparatus including means to translatean interrupted tone oi different tre'- quency received from the distant terminal into telegraph signals, means operating when the telegraph transmitting apparatus is asso- "ciated With said four-Wire junction to render said transmitting line operative andl to disable said receiving line, means connecting said telegraph receiving apparatus With said receiving line between the point at which it isf'disabled and said radio receiver, a'fsuppression dcvice'for suppressing the tone frequency supplied-by said telegraph transmitting apparatus While passing-the tone tre-U quency used for telegraph ytransmission Afrom 'i the Vdistant terminal, and means to connect said suppression device in said receiving line,

said meansv operating in response toa sus-- tained tone'ot predetermined duration and of the frequency Vsupplied by said telegraph transmitting apparatus. Y

6. vIn 'a radio signaling system including a radio transmission link, a radio transmitter and a radio receiver at one terminal of said radio link, a four-Wire junction, anormally disabled one-Way transmitting 'line VeX- tending from said four-Wire junction to said radio transmitter, a one-Way receiving line extending rfrom said radiol receiverV to'saidv f junction, means associated with each'of said lines and responsive toftelephone. signals transmitted thereover to disable the other line, telegraph transmitting apparatus and telegraph receiving apparatus, said telegraph transmitting apparatus'producin'g la tone interrupted in accordance With a code, and said telegraph receiving apparatus including means to translate anV interrupted tone of telegraph different frequency received from the distant terminal into telegraph signals, means operating when the telegraphtransmitting apparatus is associated With said four-Wire junction to render said transmitting line operative and to disable said receiving line, means connecting said telegraph receiving apparatus With said receiving line between the point at Which it is disabled and said radio receiver, a suppression device for suppressing the tone frequency supplied by said transmitting apparatus v*While passing the tone frequency used for telegraph transmission from the distant terminal, and means to connect said suppression device in said receiving line, said means operating in response to a sustained tone of predetermined duration and ofthe frequency supplied by said telegraph transmitting apparatus, said means also operating to maintain said-suppression device connected during code interruptions of said tone.

7. In a signaling system a transmission circuit, a suppression filter for suppressing undesired frequencies, and means associated With said transmission circuit and responsive to undesired frequencies-for connecting said suppression filter in said transmission circuit, said filter when so connected permitting desired frequencies to pass through it While suppressing undesired frequencies.

8. In a signaling system a transmission circuit capable of transmitting a band of voice frequencies, a suppression filter for suppressing interfering frequencies Within the voice range, and means associated with the transmission circuit and responsive to said interfering frequencies but unresponsive to voice currents for connecting said suppression fllter in said transmission circuit, said filter when so connected permitting desired frequencies to pass through it While suppressing undesired frequencies.

In testimony whereof, I have signed my name to this specification this 10th day of December, 1928.

AUSTIN BAILEY. 

